As a technique of controlling the opening of a control valve driven by an electric actuator, there is known a technique of feedback controlling the opening of the control valve to a target opening. For example, Japanese Patent Application Laid-Open No. Hei 10-288052 (hereinafter, referred to as “Patent Document 1”) discloses a technique of feedback controlling the opening of an internal combustion engine throttle valve as a control valve to a target opening. This technique detects the opening of the throttle valve by using a sensor and controls electricity supply to an electric motor as an electric actuator by a control command, which is decided by a feedback control law such as the PID law from a deviation between the detected opening and the target opening of the throttle valve.
In the technique of feedback controlling the opening of the control valve, however, as shown in Patent Document 1, the deviation between the detected value and the target opening does not become constantly zero due to a disturbance or other factors and finely fluctuates in general, for example, even if the detected value of the opening of the control valve converges substantially to the target opening in a situation where the target opening of the control valve is maintained at a constant level. Moreover, the fine fluctuation of the deviation causes a fine fluctuation of a driving force applied from the electric actuator to the control valve. Therefore, there has been a problem of wear or deterioration which easily occurs in the components of the electric actuator such as, for example, the components (gear and the like) of a power transmission system between the electric motor and the control valve, a shaft bearing which supports a movable part, and other parts to which a force is applied during operation of the electric actuator.
In view of the above background, the present invention has been provided. Therefore, it is an object of the present invention to provide a control device and a control method for a control valve capable of reducing situations where the driving force to be applied from the electric actuator to the control valve fluctuates finely to suppress the progress of the wear or deterioration of the components of the electric actuator.